Unfortunatly I have to agree with the fact that the Allies Aren't Realistic.

Only a suggestion, but you can alter these things a little bit, Imperial Guards should have Space Marines(Not functioning properly currently) and Inquisitorium.

Orks should have maybe Chaos(Nothing else, according to most lores orks never asked for help and the only time they aided chaos was in DoW1 in the campaign, I have no idea if this is legitimate I didn't dig into the subject too much)

Necrons are too powerful to have allies, they have no allies! Only the dead shall walk among the dead.

Tau should have an alliance with the Elder (As far as I know [And that's very little] they have no problems with the Eldar) and maybe with the Imperial Guards (Maybe).

Please excuse me if I'm mistaken, I have not dug into the W40k lore yet because I simply never had to, if I will have to I will though.